Thanks for showing this, I can tell by the thicker trim around the vinyl roof

Indeed this is the 1978 version of Diamond Jubilee Edition

The thicker trim and coach light were first used (and that year, exclusively) on the Diamond Jubilee Edition in 1978.

In 1979 the lamp was recycled on both the Collectors' Series and the Cartier edition of the Mark V. In fact, the quickest way to tell the '79 Cartier from the '78 is said coach light - the exterior colors didn't differ between the two years for that particular edition.